| With the improvement of modernization level on agricultural equipment, the increasing complexity of function and the improving requirements of farmers on the safety and reliable performance of agricultural equipment, the service life and reliability of agricultural equipment is becoming an urgent problem that needs to be solved. In this paper, large wheeled harvester is taken as subject. The loading characteristic, fatigue life and fatigue reliability of the frame are investigated. A new fatigue analysis model and reliability analysis model were proposed in this work. The details are as follows:(1) The load characteristics of the harvesting machinery frame under working condition is analyzed. First, the layout of the corn harvester is summarized. Then, the combined effect of the gravity center changing of each components on the load of frame is analyzed under different working conditions. Road roughness test is designed with fifth wheel gauge to obtain the elevation data of random road in the field. Road is reconstructed based on theory of harmonic superposition. The rdf text of road is generated using MATLAB. Dynamic model of the harvest machinery is constructed in the dynamic analysis software ADAMS. Load characteristics of the frame is analyzed in the random field based on reconstructed road.(2) A finite element model of the corn harvester frame is established. Load and constraints are applied based on position of all other components in the whole machine. Appropriate element type and mesh method is selected to calculate the stress distribution and the total deformation of the frame. An experiment is designed to acquire the dynamic load signals of dangerous position on corn harvester frame. The average stress under empty-load and full-load conditions was obtained and analyzed. At last, the dynamic load time curve of dangerous positon under full-load is acquired to provide data supporting the following fatigue analysis and life prediction of the frame.(3) Fatigue life of the corn harvester frame is analyzed based on power density method. Power density method overcomes deficiency of traditional fatigue analysis theory without considering the influence of load frequency, by considering the influence of both the amplitude and frequency of the stress load on the fatigue life. The fatigue life of dangerous points on the frame is calculated by power density method and SN theory method arecompared. Analysis results show that the method proposed in this paper on the corn harvest machine frame fatigue life prediction is more close to the actual working life of the frame.(4) Based on the power density theory, a new method named as power density interference model was proposed to calculate the fatigue reliability, which combined the stress-strength interference model with power density theory. The relation between the fatigue reliability and power density was deduced from the relation between the fatigue reliability and stress amplitude. Based on the power density interference model, an infinite fatigue life model was built. According to the tested power density on the frame, the frame failed to satisfy the infinite life design (95% confidence interval)... |
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